Piston pump for liquefied gas

ABSTRACT

A fuel supply system for a vehicle uses a multi-piston LPG injunction pump which pumps fluid from a storage tank to an engine. The multi-piston pump uses the vehicle&#39;s pneumatic air system, wherein the pressurized air of this system alternatingly drives at least two pistons of the piston pump. Each piston moves through a pumping stroke and a return stroke wherein one piston moves through a pumping stroke, while the opposite piston moves through a return stroke. The pump includes barrier fluid chambers surrounding each of the pistons wherein during a pumping stroke of one piston, a first barrier fluid chamber associated with the one piston decreases in volume as the piston displaces through its pumping stroke. This reduction in volume of the barrier chamber drives the barrier fluid out of the first barrier fluid chamber into a second barrier fluid chamber associated with the second piston. By driving the barrier fluid into this second chamber, this pressurizes the second chamber and effects the displacing movement of the second piston through its return stroke as the barrier fluid chamber increases in volume through the movement of the second piston.

CROSS REFERENCE TO RELATED APPLICATIONS

This application asserts priority from provisional application 61/583,430, filed on Jan. 5, 2012 which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a multi-piston pump and more particularly to a multi-piston liquid propane injection pump for a vehicle.

BACKGROUND OF THE INVENTION

In conventional diesel engines, it is known to inject liquid propane (LPG) into the fuel-air mixture in the fuel header or manifold of the engine. This is done to reduce emissions and increase performance of the vehicle. Typically, the vehicle would include an LPG tank and a pump which is in fluid communication with the LPG tank and pumps the LPG or other fluid into the engine manifold. In a known configuration, such a pump may be an in-tank, submersible turbine pump. However, such a configuration is known to have disadvantages associated therewith.

It therefore is an object of the invention to overcome disadvantages associated with the prior art.

The invention relates to a fuel supply system for a vehicle which uses an externally-mounted positive displacement pump to supply the LPG from the storage tank to the engine. More particularly, the invention relates to a multi-piston LPG injunction pump which is formed as a positive displacement pump for pumping the fluid from the storage tank to the engine intake manifold. In the preferred embodiment, the pump is provided in a dual piston configuration. The dual-piston pump is operated using the vehicle's pneumatic air system, wherein the pressurized air of this system alternatingly drives the two pistons of the dual-piston pump. The pump uses a common housing, with two piston bores in which the pistons are driven in a reciprocating manner. Each piston moves through a pumping stroke and a return stroke wherein the pistons move in opposite directions during their respective strokes. More specifically, as one piston moves through a pumping stroke, the opposite piston moves through a return stroke. The vehicle's air system is used to pressurize and drive the pistons through their pumping stroke, but is not used on the return stroke. Rather, to effect the return movement of the second piston, the pump of the invention provides barrier fluid chambers surrounding each of the pistons where each barrier fluid chamber is in fluid communication with the other. During a pumping stroke of one piston, a first barrier fluid chamber associated with the one piston decreases in volume as the piston displaces through its pumping stroke. This reduction in volume of the barrier chamber drives the barrier fluid out of the first barrier fluid chamber through a communication passage into the second barrier fluid chamber associated with the second piston. By driving the barrier fluid into this second chamber, this pressurizes the second chamber and effects the displacing movement of the second piston through its return stroke such that the barrier fluid chamber increases in volume through the movement of the second piston.

The multi-piston pump of the invention, therefore, does not require a mechanical linkage between the two pistons, and only uses a single air source that alternatingly and continuously pressurizes and drives one piston and then the other. Once the first piston is driven to the limit of its pumping stroke and the second piston has moved to the limit of its return stroke, the pressurized air that serves as the driving fluid is then turned off to the first piston and is turned on to supply driving fluid to the second piston. Thus, the single air supply will then drive the second piston through its pumping stroke wherein the function of the barrier fluid chambers causes the first piston to reverse and then move through its return stroke due to the transmission of the barrier fluid from the second barrier fluid chamber to the first barrier fluid chamber. The alternating operation of the pistons generates a continuous, uninterrupted flow of the LPG on the process fluid side of the pistons since one piston or the other is always moving through a pumping stroke.

In addition to serving as the motion-inducing force for one piston on its return stroke, the barrier fluid also serves additional functions. For example, the barrier fluid continuously lubricates the seals that are provided on the pistons which prevent leakage of the barrier fluid out of the barrier fluid chambers, as well as which seals prevent leakage of the higher pressure propane or drive air into the barrier chambers. This lubrication lengthens the life of the seals. Additionally, the barrier fluid impedes the leakage of propane past the seals and to the environment. Preferably, the invention includes leak detectors which detect the presence of the propane if it migrates into the barrier fluid or past the barrier fluid into an air discharge. Still further, this arrangement serves to dampen the tank pressure of the propane wherein the motion of the piston on its return stroke may pull a vacuum within the pumping chamber and wherein the pressure of the propane tank is offset by the barrier fluid and the restricted flow of the air being discharged on the near side of the piston moving through its return stroke.

Other objects and purposes of the invention, and variations thereof, will be apparent upon reading the following specification and inspecting the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 diagrammatically illustrates a fuel injection system including the multi-piston pump of the invention.

FIG. 2 is a perspective view of the pump.

FIG. 3 is a perspective view showing the internal components of the pump.

FIG. 4 is a side cross-sectional view as taken along line 4-4 of FIG. 10.

FIG. 5 is a side cross-sectional view as taken along line 5-5 of FIG. 10.

FIG. 6 is a side cross-sectional view as taken along line 6-6 of FIG. 10.

FIG. 7 is a side-cross sectional view of the pump housing.

FIG. 8 is a plan view of the pump housing taken from above.

FIG. 9 is a perspective view of a bottom plate of the pump assembly.

FIG. 10 is a plan view of the bottom plate.

FIG. 11 is a side cross-sectional view of the dual-piston pump in an alternate configuration.

FIG. 12 diagrammatically illustrates an alternate configuration of a fuel injection system and a single-piston pump provided therein.

FIG. 13 illustrates a further embodiment of the invention illustrating a multi-piston pump configuration with a pair of in-line pistons mechanically driven in unison.

FIG. 14 is a side cross-sectional view of the alternate pump configuration of FIG. 13, as taken along a section line angularly offset from the section line of FIG. 13.

Certain terminology will be used in the following description for convenience and reference only, and will not be limiting. For example, the words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the arrangement and designated parts thereof. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import.

DETAILED DESCRIPTION

Referring to FIG. 1, the invention generally relates to a fuel supply system 10 for a vehicle which is generally designated by reference numeral 11 in FIG. 1. This vehicle 11 may be any conventional vehicle, but typically is a truck or the like in which a supplemental fuel, such as Liquefied Petroleum Gas (LPG or propane) or an LPG/Butane mix, is injected into the engine to improve performance thereof.

As to the vehicle 11, this vehicle 11 is powered by a conventional diesel engine 12, which includes a diesel engine intake 14 that may be constructed in the form of a fuel header or manifold. This engine intake 14 is supplied through one or more fuel injectors 15 wherein a representative one of such injectors 15 is illustrated in FIG. 1. For the diesel engine 12, it is known to inject the LPG into the fuel-air mixture to reduce emissions and increase engine performance. In known systems, the LPG may be pumped using an in-tank submersible turbine pump (not illustrated). The present invention relates to an improved pump configuration used to pressurize and inject the LPG into the engine intake 14.

More particularly, a conventional vehicle may also include a supply tank 18 which is mounted to a vehicle body and is pressurized so as to store the LPG or other fuel additive therein. To deliver the injection fluid to the injectors 15 and to the engine intake 14, an inventive injection pump 19 is additionally provided which preferably is an air-driven LPG injection pump that is pneumatically driven by the air supply system 20 of the vehicle 11 as will be described in greater detail hereinafter. Since the air supply system 20 is the driving means, the pump 19 avoids the use of electric motors and other mechanical means to drive the pump 19. It will be understood that the pump 19 could also be driven by other pressurized fluid sources such as an “under the hood” air compressor on the vehicle 11, a hydraulic fluid supply system or by mechanical means such as one or more linear actuators. The particular construction of the inventive pump 19 provides a low flow, high pressure pumping of the LPG or propane. Further, the pump 19 readily accommodates changes in environmental temperature which can vary the pressure or psi of the propane depending upon whether environmental conditions are hot or cold.

Generally, as to the piping system connected between the supply tank 18, injection pump 19 and engine intake 14, these components are piped together in fluid communication with each other to define the supply lines for the delivery of LPG or any other process or injection fluid from the supply tank 18 to the engine intake 14. The piping system 21 also includes various system controls to control the delivery of the injection fluid. More particularly, the supply tank 18 is connected to the injection pump 19 by a first supply line 22 that is connected upstream of the injection pump 19 and receives the LPG or other injection fluid therethrough. Specifically, the supply line 22 includes an upstream segment 22A, a downstream segment 22B and a system shutoff valve 23 which is connected therebetween to control the flow of LPG through the supply line 22. The system shutoff valve 23 is configured for automatic control through a first control line 26 that is operatively controlled by a PLC 27 (Programmable Logic Controller) which serves as a system controller for controlling the operation of the various mechanical components and the various system controls provided therein. The system controller 27 may take other forms, such as different types of electrical or mechanical system controllers, although most preferably, a computer-based controller is provided to generate the necessary electronic signals to drive the various controls, as will be described further herein.

The system shut-off valve 23 preferably is operated by a solenoid 30 which is operatively connected to an electronic control line 26 which serves as the output from the PLC system controller 27 for effecting system shutoff. When the valve 23 is in an open operative condition, the injection fluid is able to flow through the supply line 22 from the upstream supply tank to the process fluid side of the downstream injection pump 19. The injection pump 19, during operation thereof, preferably draws the injection fluid through the supply line 22 and then pumps the fluid through another downstream supply line 32, which connects the injection pump 19 to the engine intake 14. The downstream supply line 32 exits the process fluid side of the injection pump 19 and extends to the injectors 15, which injectors 15 restrict the fluid flow there through to inject the LPG injection fluid into the engine intake 14 as diagrammatically indicated by reference arrow 32A. The injectors 15 serve to constrict the fluid flow therethrough so that the injector flow 32A essentially is pressurized and sprayed into the engine intake in an appropriate condition for use by the diesel engine 12.

Preferably, the injection pump 19 pressurizes the injection fluid to generate a specific constant pressure, which pressure is used to supply the engine intake 14 which may be in the form of a fuel header or manifold. To optimize operation of the diesel engine 12, the specific constant pressure should be maintained by operation of the system and excessive process fluid pressures are undesirable. In order to accommodate the possibility of excessive pressures within the supply line 32, the piping system 21 further includes a return line 33, which is fluidly connected to the supply line 32 upstream of the injectors 15. The return line 33 connects to a pressure bypass valve 34, which is normally closed, but opens if a pressure limit is reached and exceeded. The pressure bypass valve 34 therefore is connected to an upstream segment 33A of the return line 33, as well as a downstream segment 33B, which thereby defines the pressure bypass line 33. If the pressure bypass valve 34 encounters pressure in the upstream segment 33A which exceeds the pressure limit, the pressure bypass valve 34 then opens in response to the excessive pressure to allow the injection fluid to flow through the downstream segment 33B back to the supply tank 18. As the injection fluid flows through the bypass segment 33B, this reduces and stabilizes the line pressure to the desired specific constant pressure that is to be developed within the engine intake 14. If the excessive pressure condition continues, the pressure bypass valve 34 would maintain an open condition to allow excessive pressure to be relieved through the bypass line 33B. Should the pressure drop below the preset pressure limit of the valve 34, the valve 34 is then able to close to allow pressure to build back up within the supply line 32 and be maintained at the specific constant pressure desired for the engine intake 14. The pressure bypass valve 34 may be mechanically adjusted to set the pressure limit, although it is also possible to control the bypass valve 34 through electronic connections and settings controlled by the system controller 27.

As an example, it will be noted that the injection pump 19 typically governs or dictates the outlet pressure in line 32 by the construction of the piston area and ratios thereof. As such, in the preferred design illustrated herein, the inlet air pressure supplied by the air system 20 would be preferably set at a desired constant pressure which would then govern the desired constant outlet pressure in line 32. However, in one potential scenario, the system may be turned off which might result in an increase in temperature within the line 32. This condition may cause expansion of the process fluid in line 32 which in turn causes the undesirable increase in line pressure, which pressure increase is preferably relieved by the bypass valve 34. It will also be understood that in some situations it may be desirable to eliminate the pressure bypass line 33 and the associated bypass valve 34.

Generally as to the injection pump 19, the pump operates to supply the injection fluid through the piping system 21. In order to operate the injection pump 19, the pump 19 is connected to and is operatively driven by the air supply system 20 of the vehicle 11. The air supply system 11 preferably is already provided on the vehicle 11 such that installation of the injection pump 19 does not require substantial changes to the vehicle systems.

The air supply system 20 illustrated in FIG. 1 is preferably driven by a fluid pressurization device and most preferably an air compressor 40 which pressurizes an air supply tank 41 through an air line 42. The air supply tank 41 functions as a reservoir for storing a bulk volume of pressurized air, which volume of pressurized air is recharged through operation of the air compressor 40. The air 41 is directed downstream from the tank 41 through a supply line 42 that connects to a four-way control valve 43. The control valve 43 is actuated by a solenoid 44 for switching of the valve 43 between first and second operative conditions. A feed line 45 is connected between the valve 43 and a first connection 46 on the injection pump 19. Additionally, the valve 43 is also connected through a second feed line 47 to a second connection 48 on the pump 19.

Still further, the valve 43 connects to a discharge line 50 which passes through an air discharge restriction 51 to a discharge port 52 for discharging air to the environment. The air discharge system 51 serves to control the discharge of air from the pump 19 which also assists in controlling the rate of the return stroke of the pistons 68 and 69 as will be described further herein. When the control valve 43 is in the first operative condition, as diagrammatically shown in FIG. 1, the air supply line 42 is connected to the feed line 45 which in turn supplies pressurized air to the injection pump 19. The second feed line 47 passes through the valve 43 and connects to the discharge line 50 to allow air to be discharged from the injection pump 19 for discharge to atmosphere. The four-way valve 43 also is moveable by the solenoid 44 to the second operative position wherein the air supply line 42 then connects to the feed line 47, while the other feed line 45 connects to the discharge line 50 for the discharge of air therethrough. Hence, the valve 43 alternatingly supplies air to the injection pump 19 through either the connector port 46 or connector port 48 while the other of the connector ports 46 or 48 is connected to the discharge line 50. Switching of the valve 43 by the solenoid 44 then reverses the connections. Operation of the valve 43 is effected by the PLC controller 27 through a control line 55 which serves as an output from the PLC 27 in order to selectively activate the solenoid 44.

Accordingly, the PLC 27 is able to control switching of the valve 43 between the first and second operative positions and thereby control operation of the injection pump 19 as will be described further hereinafter.

As will be understood in additional detail in the following discussion of FIGS. 2-6, the injection pump 19 also has an outlet port 57 which connects to a barrier fluid pressure line 58 through which a barrier fluid (discussed hereinafter) is able to flow to a pressure switch 59. The pressure switch 59 is formed as part of an electronic control loop 60 which monitors the pump 19 for an overpressure in the barrier fluid pressure. The barrier fluid pressure is diverted through the fluid pressure line 58 to the pressure switch 59 and mechanically operates the switch 59 to close the electrical connection within the monitoring circuit 60. This provides an indication whether an excessive barrier fluid is encountered within the injection pump 19, the full understanding of which will become apparent upon a reading of the following discussion. If an overpressure condition exists, the pump 19 typically would be shut down for maintenance and repair.

Turning next to FIGS. 2-4, the injection pump 19 is illustrated separately from the remaining system components described relative to FIG. 1. Generally, the injection pump 19 is formed as a dual-piston pump that functions as a positive displacement pump that is mounted on the vehicle external to the LPG supply tank 18. The dual-piston pump 19 is operated using the vehicle's pneumatic air system 20 wherein the pressurized air of this system alternatingly drives the dual-piston configuration of this pump 19 to generate a continuous flow of process fluid to the injector(s) 15.

The pump 19 comprises an outer housing 60 that is preferably formed as an assembly which includes the housing body 61, a top or cover plate 62 and a bottom plate or valve body 63. Preferably, the outer housing is formed of cast iron or other structurally rigid material and has a mount 63A with fastener bores 63B for mounting the pump 19 to the vehicle frame. Internally of the housing body 61, the housing body 61 defines at least two piston bores 66 and 67 which each receive a respective, dual-area piston 68 and 69 therein. Generally, each of the pistons 68 and 69 move through a linear pumping stroke and return stroke wherein the pistons 68 and 69 move in opposite directions during their respective strokes. More particularly, as one piston 68, for example, moves through a downward pumping stroke, the opposite piston 69 moves upwardly through its respective return stroke. As will be described herein, the vehicle's air system 20 is used to pressurize and drive the pistons 68 and 69 through their respective pumping stoke, but is not used on the return stroke. Rather, as one such piston 68 or 69 is moving through its pumping stroke, the other, or second piston, is returned upwardly by a barrier fluid configuration which operatively drives the second piston through its return stroke. The configuration of the barrier fluid and air system also assists in dampening the return stroke of each piston 68 and 69 and counters the pressure of the propane tending to push the pistons 68 and 69, such that the barrier fluid and air discharge serve to control the rate of the return stroke. The barrier fluid configuration will be described in further detail hereinafter.

Referring to FIGS. 7 and 8, the housing body 61, a first housing section 71 and a second housing section 72 are disposed vertically, one above the other, although it will be understood the pump 19 need not be oriented in this vertical orientation to operate. The bottom or lower housing section 71 includes two parallel bore sections 73 which open downwardly from the bottom of the housing body 61 and terminate at an annular housing shoulder 74 on the interior or upper end of such piston bore sections 73. The bottom end of the first housing section 71 defines a bottom housing face 75, which includes a pair of annular sealing gaskets 76 surrounding the bore sections 73 for defining a fluid tight seal when the bottom plate 63 is secured to the housing body 61 to essentially close off the bottom open ends of the piston bores 66 and 67. The housing section 71 also includes a pair of radially extending connector flanges 77 which each include a respective fastener bore 78 for receiving a threaded fastener 79 (FIGS. 2 and 4) for securely affixing the bottom plate 63 to the housing body 61.

As to the upper housing section 72, this housing section 72 also includes a pair of parallel piston bore sections 80 which open vertically from a top housing face 81 of the housing section 72. The bore sections 80 terminate at their bottom ends at the annular step-like housing shoulder 74. As such, the bore sections 80 have a greater diameter than the bore sections 73 to thereby define the annual shoulder 74 best shown in FIG. 7. The top housing face 81 also includes respective annular sealing gaskets 82 which surround and seal the piston bore sections 80 when the top plate 62 is secured thereto. The upper end of the housing section 72 also includes six radially projecting fastener flanges 84 which include respective bores 85 that receive the threaded fasteners 86 vertically therethrough. With this construction, each of the piston bores 66 and 67 is defined by annular bore surfaces 66A and 67A, having a cylindrical, stepped shape wherein the bottom bore sections 73 are coaxially aligned with the upper bore sections 80 along common center axes 88 as shown in FIG. 7. As previously mentioned, the diameter of the bore sections 73 is smaller than the diameter of the upper bore sections 80. Proximate the junction between these bore sections 73 and 80, the housing body 61 includes a respective fill port 90 for each bore 66 and 67 which fill port 90 is normally closed by a removable, threaded plug 91 (seen in FIGS. 2-4). These fill ports 90 are provided for filling of a barrier fluid into the housing body 61.

Additionally, the housing body 61 is provided with an intermediate, balancing passage 93 that is formed so as to extend completely through an intermediate divider wall 94 that is defined between the piston bore sections 80 and 73. This balancing passage 93 extends horizontally or laterally through the divider wall 94 and has one end in open connection with the first piston bore 66 and the opposite open end in fluid communication with the piston bore 67 on the opposite side of the divider wall 94.

Referring to FIGS. 3 and 4, the pistons 68 and 69 have identical constructions and the description of these pistons in the following discussion will use common reference numerals to reference common parts thereof. Generally, the pistons 68 and 69 are positioned within the piston bores 66 and 67 respectively for reciprocating vertical movement between the lower most pumping stroke position (see piston 68) and the upper most refracted position (see piston 69). These pistons 68 and 69 are axially or linearly slidable within their respective piston bores 66 and 67 between these two positions which define the limits of travel for the downward pumping stroke, or the upward return stroke.

During assembly, the pistons 68 and 69 are slidably fitted through the open upper end of the housing section 72 and then are captured within the housing 61 by the installation of the top plate 62 and bottom plate 63 as will be described further herein. It will be noted that the pump construction of FIG. 3 functionally is the same as the construction of FIG. 4, although there are some differences in the overall profile of the individual components. However, the discussion herein makes no specific distinction between FIGS. 3 and 4, with it being understood that FIG. 4 and the remaining figures illustrate the preferred and specific instruction of the invention.

Referring to the piston 68, the piston 68 has a cylindrical shape, defined by a major piston face 95 and a minor piston face 96 wherein these faces 95 and 96 are differentiated by their respective diameters and respectively define the driven or air side of the piston 68 and the pumping or process side of the piston 68. The major piston face 95 has a larger diameter than the minor piston face 96 wherein the respective diameters are defined by a major cylinder surface 97 and the minor cylinder surface 98. The major cylinder surface 97 extends partially along the axial length of the piston 68 and abrupt steps or extends radially inwardly to the minor cylinder surface 98 to thereby define an annular step or shoulder 99. The differences in diameters results in an increase or amplification of pressure between the drive side of the pistons 68 and 69 and the pumping side of the pistons 68 and 69. For example, the pressurized air that drives the pistons 68 and 69 may be about 100 psi while the output pressure from the pump 19 through the discharge line 32 may be up to 178 psi, which is the feed pressure desired for feeding the injectors 15. In this manner, the outlet pressure from the pump 19 which defines the feed pressure can be governed or controlled by selectively defining the air input pressure. Additionally, the output pressure may also be designed through selectively constructing the pistons 68 and 69 and the ratio of the major piston face 95 to the minor piston face 96 of each piston 68 or 69. By selectively choosing the diameter ratio, or dimensional ratio between these piston faces 95 and 96, the ratio of the input pressure to the output pressure can be selectively designed into the pump 19. Secondarily, the outlet pressure of the pump 19 can be further adjusted by selectively choosing the input pressure of air that is used to drive the piston 68 and 69.

Next as to the barrier fluid configuration referenced above, the radial dimension of the piston shoulder 99 is proximate to the radial width of the housing shoulder 74 wherein the surfaces of the respective shoulders 74 and 99 are disposed in axially facing relation. The pistons 68 and 69 move axially relative to each other so that the piston shoulder 99 both moves toward the housing shoulder 74 and then moves away from such shoulder 74 during pump operation. As a result, the surfaces of the shoulders 74 and 99 define the axial boundaries of an annular barrier fluid chamber 101. More specifically, the barrier fluid chamber 101 extends annularly about the minor cylindrical surface 98 of each piston 68 and 69, and is thereby defined radially between the piston surface 98 and the opposing housing surface 102, and is defined axially between the housing shoulder 74 and the opposing piston shoulder 99. Due to the relative movement of these shoulders 74 and 99 toward and away from each other, the total volume of the barrier fluid chambers 101 varies, i.e. increases and decreases as the piston 68 and 69 reciprocate through their pumping and return strokes.

Each of these barrier fluid chambers 101 is in fluid communication with each other through the intermediate balancing passage 93 described previously and each of said chambers 101 includes a barrier fluid therein which fills the total volume of the two barrier fluid chambers 101 and the passage 93. The barrier fluid may be a suitable oil or other liquid or in some conditions might be supplied as a gas. Preferably, the barrier fluid is a liquid that is both non-compressible and has lubricating properties. The barrier fluid therefore lubricates the pistons and their piston bores 66 and 67, and serves as the hydraulic means for returning the pistons 68 or 69 to their retracted position at the end of the return stroke. The barrier fluid is supplied to these chambers 101 through the fill ports 90 and their associated plugs 91.

The barrier fluid is sealed within such chambers 101 by the provision of annular piston rings or seals 105 and 106 which prevent the barrier fluid from migrating along the major and minor cylindrical surfaces 97 and 98 of the pistons 68 and 69 and thereby leaking past the major and minor piston end faces 95 and 96. Preferably, the seals 105 and 106 are formed of any suitable material which will maintain contact with the interior surfaces of the piston bores 66 and 67. In the preferred embodiment, the seals 105 and 106 have a generally U-shaped cross-section which defines an annular grove or channel within the seals 105 and 106 which channels open axially towards the high pressure sides of the piston 68/69. More specifically, the channel of the seal 105 preferably would open actually upward (FIG. 4) towards the air supply so that the air supply may migrate into the channel of the seals 105 and effectively spread the seals radially to improve the radial contact between the seals 105 and the opposing surfaces of the piston 68/69 and the bore surfaces 66A and 67A. The other seals 106 would have their respective channels opening axially downwardly towards the higher pressure propane located within the pumping chambers. The intermediate barrier fluid would be at a lower pressure relative to the air and the propane, such that the higher pressure at the opposite ends of the pistons 68/69 would improve the sealing being created by the seals 105 and 106.

Further, one advantage of the barrier fluid between the seals 105 and 106 is that the barrier fluid also acts to lubricate the seals 105 and 106 and increase the operating life thereof before the seals 105 and 16 undergo wear and any leakage occurs.

The barrier fluid chambers 101 generally are provided to cause automatic return of a non-driven piston 68 or 69 in response to driving movement of the other of the pistons 68 or 69. As will be described in further detail hereinafter, driving movement of one piston, such as piston 68 through its pumping stroke in the downward direction reduces the volume of the first barrier fluid chamber 101 and drives the barrier fluid out of this first chamber 101 through the passage 93 and into the other of the barrier fluid chambers 101. This other or second piston 69 is in a condition where it is no longer driven by the vehicle air system 20 and as such is able to freely move in the opposite direction through its return stroke. Hence, by reducing the volume of the first barrier fluid chamber 101 associated with the driven piston 68, the chamber volume decreases and drives the barrier fluid into the second chamber 101 of the other piston 69 which increases the pressure and thereby drives the second piston 69 upwardly through the return stroke. Hence, only one of the two pistons 68 and 69 needs to be driven by the air system 20, while the other piston is passively driven through its return stroke by the provision of the interconnected barrier fluid chambers 101 and balancing passage 93.

The volume of barrier fluid in the chambers 101 preferably has a fixed non-variable volume. The pressure of the barrier fluid is monitored in the control system of FIG. 1 by the provision of a barrier fluid pressure line 58 which connects to the housing 60 by the connector 57 as shown in FIG. 1. The connector 57 includes at least one outlet port which is in open communication with any of the barrier fluid chambers 101 or passage 93 and allows the barrier fluid to flow or pass through the line 58 to the pressure switch 59. Hence, in the event that leakage of fluid into the barrier fluid chambers 101 occurs past the seals 105 and 106, the barrier fluid pressure line 58 and associated pressure switch 59 allow the PLC 27 to monitor the barrier fluid and detect a barrier fluid over-pressure condition. This may occur if there is a failure of the seals 105 or 106 on the drive side or the process side of the pistons 68/69 which would increase the fluid volume in the barrier fluid chambers 101 and thereby increase the pressure therein.

In addition to the lubricating benefit provided by the barrier fluid, the barrier fluid also serves as an intermediate barrier to prevent leakage of the propane out of the system to the ambient environment. In this regard, if the propane were to leak past the seals 105 and 106, the propane could then escape through the discharge port 52. As an additional or redundant leak-detection mechanism, a propane sensor or detector may be included within the system to detect the presence of propane or other contaminants within the barrier fluid. For example, the fluid pressure line 58 may be provided with a sensor 108 (see FIG. 1) which would detect the presence of propane or other contaminants within the barrier fluid itself. This sensor 108 would thereby detect leakage into the barrier fluid, for example, past the seals 106. This provides a first line of defense against leakage by detecting leakage of propane past the seals 106 and preferably before such leakage occurs past the seals 105. Additionally, or in the alternative, a sensor 109 may be provided in the discharge line 47 which would thereby detect the presence of contaminants such as propane after such contaminants had leaked past the seal 105, but before such contaminants were discharged to any significant extent through the discharge port 52. These sensors 108 and 109 could be provided alone or in combination together so as to monitor both the barrier fluid as well as the air being discharged through line 47.

To effect driving of the pistons 68 and 69, the top plate 62 is provided with the air supply connections 46 and 48 which connect to the air supply lines 45 and 47 discussed above. These air supply connections 46 and 48 define air passages through the top plate 62 which permit the application of the pressurized air from the air system 20 selectively to either the piston bore 66 or alternatively, to the piston bore 67. The above-described control valve 43 controls the application of the pressurized air first to the piston bore 66, and then to the piston bore 67. When air is being supplied to one of such piston bores 66 or 67, the other piston bore 66 or 67 is open to environment to allow the air to vent or escape through the discharge line 50.

If desired, the respective piston 68 and 69 also may be provided with blind bores 115 to assist in movement of the pistons 68 and 69, as will be described further herein.

To control the time at which the valve 43 switches between the first and second operative conditions, the bottom housing plate 63 is provided with two proximity sensors 116-1 and 116-2 that have respective electrical sensor lines 117-1 and 117-2 (FIG. 4) which connect to the PLC 27 as shown in FIG. 1. These proximity sensors 116-1 and 116-2 are able to detect the piston 68 or 69 as it approaches the sensor 116-1 or 116-2. In one example, the minor piston face 96 may be provided with a metallic insert or plug 118-1 or 118-2 which preferably is formed as a magnet and is detected as it approaches the proximity sensor 116-1 or 116-2 to trip the proximity switch therein. In this regard, the sensor 116-1 and 116-2 may be of the type, such as a Reed switch, that detects the presence of magnetic body when the piston 68/69 and sensor 116-1/116-2 are close together, for example, as seen in FIG. 4, wherein the piston 68 is disposed in close adjacent relationship to the sensor 116-1. Theses sensor inserts 118-1 and 118-2 seat within respective sensor bores 119 and the pistons 68 and 69 as seen in FIG. 3. Preferably, the sensors 116-1 and 116-2 are positioned centrally within the bottom of the piston bore 66 and 67 so as to be concentrically aligned with the piston 68 and 69 and their respective sensor bores 119.

While the proximity sensors are illustrated as a preferred embodiment for reversing the movement of the pistons 68/69, other sensing or control means may be used to reciprocate these pistons 68/69. One example, the PLC may simply control the solenoid 44 using a timing signal or circuit wherein the valve 43 may be switched between its operative conditions after preselected time periods which are calculated based upon the time that each piston 68/69 moves through their respective pumping and return strokes. Preferably, the time period as selected serves to limit or prevent bottoming out of the pistons 68/69 against the housing 60. Other methods may be used to determine the time or location at which the piston stroke should be reversed. For example, it also may be desirable to monitor the discharge pressure in line 32 which would indicate when the pump bottoms out wherein detection of a pressure drop in such line 32 would indicate that one-piston had reached the end of its pumping stroke.

As seen in FIG. 4, the sensor 116-1 in the illustrated position detects the piston 68 which provides the signal through sensor line 117-1 to the PLC 27, which PLC 27 in turn sends a control signal through control line 55 to the solenoid 44 which in turn switches the valve 43 between the first operative position shown in FIG. 1 to the second operative position described above. Upon the switching of the valve 43, the supply of pressurized air to the connector 46 is discontinued and this connector 46 is then allowed to discharge through discharge line 50 with the valve 43 in the second operative position. In this condition, the pressurized air is then supplied from line 42 to line 47 which supplies the pressurized air to the connector 48. This now drives the piston 69 downwardly through its pumping stroke which continues until its respective sensor 116-2 detects the presence of the piston 69 which then causes the next successive switching of the valve 43 to then depressurized piston 69 and re-pressurize piston 68. As the piston 69 was moving through the pumping stroke, its respective barrier fluid chamber 101 decreased in volume which drove the barrier fluid through the intermediate passage 93 into the second barrier fluid chamber 101 which simultaneously causes the non-driven piston 68 to be displaced upwardly through its return stroke. Since this return stroke of the piston 68 reduces the volume of the piston bore 66 defined between the major end face 95 and the opposing top plate 62, the decreasing volume of this piston bore 66 adjacent the connector 46 decreases and pushes the depressurized air through connector 46 to the discharge line 50. By selectively reversing the valve 43, one piston or the other is actively driven while the other piston is passively refracted through the barrier fluid cooperating therebetween.

In this manner, the pistons 68 and 69 are hydraulically connected to each other and able to reciprocate simultaneously with each other without the need for any mechanical linkages therebetween. Further, the system only requires that one piston or the other piston be actively driven with the non-driven piston being automatically returned through its return stroke.

To further describe the pumping of the LPG or other fuel additive by the injection pump 19, the following discussion describes the pumping of this injection fluid during the reciprocating movement of the piston 68 and 69 described above.

Referring to FIGS. 5, 6, 9 and 10, this pumping is accomplished through the structure of the bottom plate 63. As previously described, the bottom plate includes the sensors 116-1 and 116-2 which are centrally located at the bottom of the piston bores 66 and 67 and are fixedly mounted to the bottom plate 63 of the housing 60. This bottom plate 63 further is provided with an elongated inlet passage 121 which connects to the supply line 22 (FIG. 1) and a discharge passage 122 which connects to the supply line 32 (FIG. 1). The inlet passage 121 (FIGS. 6 and 10) includes controlled inlet ports 123-1 and 123-2 which include check valves that permit one-way in-flow of the LPG process fluid into the piston bores 66 and 67, but automatically close when pressurized to prevent discharge or out-flow of any process fluid from the bottom ends of the piston bores 66 and 67.

More particularly, these piston bores 66 and 67 respectively define at the bottom ends thereof piston chambers 124 and 125 that have variable volumes and are defined axially between the minor piston face 96 and the plate surface 127 of the bottom plate 63. Hence, as one of the pistons 68 and 69 is moving through a pumping stoke, such as piston 68, its respective check valve in inlet port 123-1 is closed. While the other piston 69 moves through its return stroke, this creates suction within the pumping chamber 125 to draw the fuel additive through the inlet passage 121 and through the open check valve in port 123-2. Hence, these check valves in ports 123-1 and 123-2 are normally closed under pressure, but open when a vacuum is formed in either of the pumping chambers 124 or 125. When encountering such vacuum, the upward movement of one piston or the other essentially refills the pumping chamber 124 and 125 with LPG process fluid until the pistons 68 and 69 switch or reverse their directions of movement.

The air discharge restriction 51, as described above, serves to throttle the exhausted air being discharged to the environment through the discharge port which throttling or restriction thereby provides control to the return stroke of the pistons 68 and 69. This reduces the pressure drop on the inlet side of the pump to insure that the liquid propane remains in the liquid state.

Referring to FIGS. 5, 9 and 10, the bottom plate 63 also includes the outlet passage 122 that communicates with the pumping chambers 124 and 125 through respective outlet ports 129-1 and 129-2 which ports are controlled by check valves. The check valves of these outlet ports 129-1 and 129-2 operate opposite to the above described check valves in that the check valves in ports 129-1 and 129-2 are normally closed when a vacuum is applied thereto to prevent in-flow, but open in response to pressure within the pumping chambers 124 and 125 to permit out-flow. Hence, as the piston 68 moves downwardly through its pumping stroke, this will open the outlet port 129-1 so that the process fluid can flow through the outlet passage 122 to the supply line 32 for subsequent injection into the engine intake 14 described above. The other outlet port 129-2, however, is in a closed condition during the return stroke of the other piston 69. In other words, as the piston 68 moves through its pumping stroke, the inlet port 123-1 is closed, but the outlet port 129-1 is open, which therefore pumps the fuel additive into the outlet passage 122. The other pumping chamber 124 is refilling at this point, wherein the outlet passage 129-2 is closed while the inlet port 123-2 is open to allow refilling of the chamber 125. When the piston 68 and 69 reverse their directions of movement, the pumping chamber 125 then discharges the volume of fuel additive therefrom through the outlet port 129-2 while the inlet port 123-2 is closed. At this time, the other pumping chamber 124 refills upon opening of the inlet port 123-1 while the respective outlet port 129-1 is closed. In this manner, the reciprocating movement of the piston 68 and 69 effect simultaneous refilling and pumping through the respective inlet passage 121 and outlet passage 122. This therefore provides pressure of fuel additive being supplied through the supply line 32 to the engine intake 14.

Referring to FIG. 11, it may be desirable to generate an assisting force which assists the initial movement of the piston 68 and 69 when they are located closest to the top plate 60. This may provide an advantage in extreme cold applications. In this regard, a coil spring 130 may be provided in each blind bore 115 of the piston 68 and 69. Normally, this compression spring 130 or other similar biasing member is in an extended, undeformed condition, as shown in piston 68. As the piston, such as piston 69, returns through its return stroke to the limit of travel against the top plate 62, the biasing member 130 is compressed which generates a biasing force acting downwardly on the piston 69 and acting to bias the piston 69 away from the top plate 62. The pressure generated within the barrier fluid chambers 101 generates a return force displacing the piston 69 upwardly that is greater than the biasing force, and as such, the piston 69 is still able to move through its return stroke unimpeded by this spring 130. However, upon a switching of the pressurization from one piston bore 66 to the other piston bore 67, the release of pressure on the piston bore 66 allows the spring 130 within the piston 69 to start to displace the piston 69 downwardly through its pumping stroke. This insures immediate movement of the piston 69 as the piston bore 67 is being repressurized through the valve 43. This insures that there is minimal to no lag of movement between the pistons 68 and 69 during the switching step.

Another advantage of the above design relates to an improved ability to refurbish the pump 19. In this regard, the top plate 62 can be readily removed to allow for replacement of the seals 105 and 106 or the various gaskets 75 and 82. Also, the bottom plate 63 is similarly removable which allows for ready replacement of the sensors 116-1/116-2 and the valves in the inlet ports 123-1/123-2 and outlet ports 129-1/129-2.

Referring to FIG. 12, a further embodiment of the invention is illustrated. This system is the same in most respects to the system illustrated in FIG. 1, and as such, common reference numerals are used for common components already described above. The use of the same reference numerals indicates that the structure and function of these components are the same and as such, further discussion of the system components is not repeated herein relative to FIG. 12. The following discussion therefore is directed to the differences in the systems of FIGS. 1 and 12.

Most significantly, the system of FIG. 12 includes a single piston pump 19A which is constructed according to the invention. In this regard, the pump 19A only has a single piston such as piston 68A. The pump 19A is structured so as to have only a single one of the pistons of pump 19 in FIG. 4 wherein pump 19A can be constructed simply by modifying the housing 60 so to form a housing 60A which only has a single piston bore 66A and piston 66A while maintaining the same arrangement shown in the above figures of an air inlet 46A, propane inlet and outlet 123A/124A, proximity sensor and the remaining components described above. The single piston 68A would still have its respective barrier fluid chamber but the intermediate passage 93 and the second piston bore and its piston would be omitted. Essentially, the pump 19A would operate similar to pump 19 except for the differences described below. Similar reference numerals are used hereinafter to indicate common structures but are designated with reference letter A to differentiate the single piston design from a design having two or more pistons.

More particularly, the pump 19A has feed line connection 46A which allows for the flow of air into and out of the piston bore. This connection 46A connects to feed line 45A that connects to a valve 43A. The feed line 45A is operatively connected to the discharge line 50 when the valve 43A is in the first operative position shown, and connects to the air supply line 42 when the valve 43A is in the second operative position after switching by the PLC-controlled solenoid 44. When the feed line 45A is connected to the air supply line 42, the pump 19A has its piston move through the pumping stroke as described above, and when connected to the discharge line 50, the pump 19A discharges air to the discharge port 52.

The supply tank 18 connects to the pump 19A at the inlet port 123-1A and the propane is pumped out of the pump 19A through the outlet port 129-1A. The inlet port 123-1A and outlet port 129-1A are controlled by the check valves previously described above, and where desired a proximity sensor or other similar sensor may also be provided to control switching of the valve 43A

The pump 19A further has a barrier fluid chamber constructed the same as that described above, which chamber connects to the barrier fluid pressure line 58 through the outlet port 57A. Since the pump 19A has the barrier fluid chamber sealed by the gaskets 105A and 106A in the same manner as described above, the barrier fluid serves the same functions of lubricating the seals 105A and 106A of the pump 19A, and the air discharge restrictor 51 throttles or controls the discharge of air through connector 46A and thereby controls the return stroke of the piston 66A.

The barrier fluid also serves the same function of resisting leakage of propane since it defines a fluid barrier intermediate or between the propane side and the air side of the piston 66A, which air side discharges to atmosphere. The system of FIG. 12 is protected by both an overpressure switch 59 which would trigger upon unwanted increases in the volume of the barrier fluid by leakage of air or propane into the barrier fluid, and is further protected by the sensors 108 and 109 which respectively monitor for the presence of propane leakage in the barrier fluid and in the air discharge.

The most significant difference results from the elimination of the second piston which would be used to effect the return stroke of the first piston. In the single-piston design, the return of the piston 66A is effected by the pressure of the barrier fluid and/or the propane or other fluid being pumped. In this regard, the propane would have a fluid pressure that would tend to drive the piston 66A through the return stroke when the drive pressure was deactivated such as by depressurization. Additionally, the system of FIG. 12 includes an accumulator 140 which is fluidly connected to the barrier fluid line 58 at connection 141. The accumulator 140 serves as a fluid reservoir for the barrier fluid as the piston 66A moves through the pumping stroke, which stroke will decrease the volume of the barrier fluid chamber as previously described and will push fluid out to the accumulator 140. The barrier fluid will generate of fluid pressure when stored within the accumulator 140, particularly where the accumulator 140 is provided with additional means for generating the barrier fluid pressure. As such, when the piston 66A is free to move through its return stroke after the switching of the valve 43A, the barrier fluid can reenter the barrier fluid chamber and serve to bias the piston through its return stroke. Additionally, any pressure in the propane would also tend recharge the pumping chamber and drive the piston 66A through the return stroke. If desired, a mechanical drive, such as a linear actuator, could be connected to the piston 66A to effect a manual reciprocating driving of the piston 66A as it reciprocates through its pumping and return strokes.

Since the pump 19A would cycle through the pumping stroke which would discharge pressurized propane through the outlet port 129 and then through its return stroke which would not effect pumping of propane, the system of FIG. 12 also preferably includes a propane accumulator 144 which connects to the downstream supply line 32 and minimizes pulsation of the fluid flow in the supply line 32. This accumulator 144 would receive a volume of the propane during the pumping stroke and discharge propane to line 32 during the return stroke to dampen fluctuations in the flow of propane into the engine intake 14.

In this embodiment, a single piston pump is provided which still possesses many of the advantages of the buffer fluid that are found in the multi-piston design.

Referring to FIGS. 13 and 14, a further embodiment is illustrated wherein this multi-piston pump 19B would replace pump 19 in the system of FIG. 1. In this regard, the pump 19B essentially connects to most of the same connections as pump 19, except that the air drive system is not needed and is replaced with a mechanical drive system 150. As will be described further, the mechanical drive system 150 may be any type such as the linear actuator 151 shown herein, which actuator 151 comprises a drive motor 152 and a double-ended drive screw 153 which simultaneously drives or operates the dual-piston, in-line configuration.

The injection pump 19B is formed as a dual-piston pump that functions as a positive displacement pump and is described herein separate from the remaining system components of FIG. 1. Unlike pump 19 which is operated using the vehicle's pneumatic air system 20, the pump 19B uses the actuator 151 to generate a continuous flow of process fluid to the injector(s) 15. The pump 19B comprises an outer housing 60B that is preferably formed as an assembly which includes two axially-aligned housing bodies 61B which are joined together in end-to-end relation, wherein the opposite ends are closed by end plates 63B. Internally, the housing bodies 61B define two in-line piston bores 66B and 67B which each receive a respective, dual-area piston 68B and 69B therein. Generally, each of the pistons 68B and 69B move through a linear pumping stroke and return stroke wherein the pistons 68B and 69B move in the same direction when moved by the actuator 151. The wide ends of the pistons 68B and 69B are connected to the opposite ends of the drive screw 153 wherein the drive screw 153 reciprocates axially by the motor drive 152 to displace the pistons 68B and 69B axially through their pumping and return strokes. More particularly, as one piston 68B, for example, moves through a leftward pumping stroke, the opposite piston 69B moves leftwardly through its respective return stroke.

In this pump 19B, the barrier fluid configuration is provided similar to that described above. In this regard, the housing body 61B is provided with an annular step 74B, and includes at least one intermediate, balancing passage 93B that is formed so as to extend axially along the housing wall 94B between the piston bores 66B and 67B. The illustrated embodiment uses two balancing passages 93B located on diametrically opposite sides of the housing 60B. Each balancing passage 93B has one end in open connection with the first piston bore 66B and the opposite open end in fluid communication with the piston bore 67B.

Referring to the pistons 68B and 69B, the pistons 68B and 69B have a cylindrical shape, each defined by a major piston face 95B and a minor piston face 96B wherein these faces 95B and 96B are differentiated by their respective diameters and respectively define the mechanically driven side of the pistons 68B and 69B and the pumping or process side of the pistons 68B and 69B. The pistons 68B and 69B have a step along the length to thereby define an annular step or shoulder 99B which is disposed in axially opposing relation with the respective housing shoulder 74B.

Next as to the barrier fluid configuration, the pistons 68B and 69B move axially relative to each other so that the piston shoulder 99B both moves toward the housing shoulder 74B in the pumping stroke and then moves away from such shoulder 74B in the return stroke. As a result, the surfaces of the shoulders 74B and 99B define the axial boundaries of an annular barrier fluid chamber 101B. More specifically, the barrier fluid chamber 101B is defined radially between the pistons 68B and 69B and the opposing housing wall 94B, and is defined axially between the housing shoulder 74B and the opposing piston shoulder 99B. Due to the relative movement of these shoulders 74B and 99B toward and away from each other, the total volume of the barrier fluid chambers 101B varies, i.e. increases and decreases as the pistons 68B and 69B reciprocate through their pumping and return strokes.

Each of these barrier fluid chambers 101B is in fluid communication with each other through the intermediate balancing passage 93B described previously and each of said chambers 101B includes a barrier fluid therein which fills the total volume of the two barrier fluid chambers 101B and the passage 93B. As described previously, the barrier fluid may be a suitable oil or other liquid or in some conditions might be supplied as a gas. Preferably, the barrier fluid is a liquid that is both non-compressible and has lubricating properties. The barrier fluid therefore lubricates the pistons 68B and 69B and their piston bores 66B and 67B, and serves as a barrier to the leakage of propane process fluid.

The barrier fluid is sealed within such chambers 101B by the provision of annular piston rings or seals 105B and 106B which prevent the barrier fluid from migrating along the pistons 68B and 69B and thereby leaking past the major and minor piston end faces 95B and 96B. One advantage of the barrier fluid between the seals 105B and 106B is that the barrier fluid also acts to lubricate the seals 105B and 106B and increase the operating life thereof before any leakage occurs.

During operation, the driving movement of one piston, such as piston 68B through its pumping stroke in the leftward direction reduces the volume of the first barrier fluid chamber 101B and drives the barrier fluid out of this first chamber 101B through the passage 93B and into the other of the barrier fluid chambers 101B surrounding piston 69B. In this embodiment, the pistons 68B and 69B are mechanically interconnected by the shaft 153 and are driven in unison by the motor drive 152.

Like the prior embodiments, the volume of barrier fluid in the chambers 101B preferably has a fixed non-variable volume, and the pressure of the barrier fluid can be monitored in the control system of FIG. 1 by the provision of a barrier fluid pressure line 58 which connects to the housing 60B in the same manner as shown in FIG. 1. The pressure line 58 would be in open communication with any of the barrier fluid chambers 101B or passage 93B and allows the barrier fluid to flow or pass through the line 58 to the pressure switch 59. Hence, in the event that leakage of fluid into the barrier fluid chambers 101B occurs past the seals 106B, the barrier fluid pressure line 58 and associated pressure switch 59 allows the PLC 27 to monitor the barrier fluid and detect a barrier fluid over-pressure condition. This may occur if there is a failure of the seals 106B on the process side of the pistons 68B/69B which would increase the pressure in the barrier fluid chambers 101B Like the prior embodiments, in addition to the lubricating benefit provided by the barrier fluid, barrier fluid also serves as an intermediate barrier to prevent leakage of the propane out of the system to the ambient environment. In this regard, if the propane were to leak past the seals 106B, the propane could then migrate into the barrier fluid. As an additional or redundant leak-detection mechanism, a propane sensor or detector may be included within the system to detect the presence of propane or other contaminants within the barrier fluid. For example, the fluid pressure line 58 may be provided with a sensor 108 (see FIG. 1) which would detect the presence of propane or other contaminants within the barrier fluid itself. This sensor 108 would thereby detect leakage into the barrier fluid, for example, past the seals 106B.

To effect driving of the pistons 68B and 69B, the actuator 151 is controlled by the PLC 27 to reciprocate the drive screw 153 in opposite axial direction. To control the time at which the actuator 151 switches the direction of shaft movement, the end housing plate 63B is provided with two proximity sensors 116-1B and 116-2B that have respective electrical sensor lines which connect to the PLC 27 previously shown in FIG. 1. These proximity sensors 116-1B and 116-2B are able to detect the piston 68B or 69B in the same manner as described above. Alternatively, the PLC may simply control the actuator 151 using a timing signal or circuit

Pumping of the process fluid is accomplished through the reciprocating movement of the pistons 68B and 69B. In this regard, the housing wall 94B further is provided with an elongated inlet passage 121B which connects to the supply line 22 (FIG. 1) at port 156 and a discharge passage 122B which connects to the supply line 32 (FIG. 1) at port 157. The inlet passage 121B includes controlled inlet ports 158 which include check valves that permit one-way in-flow of the LPG process fluid into the piston bores 66B and 67B, but automatically close when pressurized to prevent discharge or out-flow of any process fluid from the ends of the piston bores 66 b and 67B.

More particularly, these piston bores 66B and 67B respectively define at the bottom ends thereof piston chambers 124B and 125B that have variable volumes and are defined axially between the minor piston face 96B and the end plate 63B. Hence, as one of the pistons 68B and 69B is moving through a pumping stoke, such as piston 68B, its respective check valve in inlet port 158 is closed. While the other piston 69B moves through its return stroke, this creates suction within the pumping chamber 125B to draw the fuel additive through the inlet passage 121B and through the open check valve 158. Hence, these check valves 158 are normally closed under pressure, but open when a vacuum is formed in either of the pumping chambers 124B or 125B. When encountering such vacuum, the upward movement of one piston or the other essentially refills the pumping chamber 124B and 125B with LPG process fluid until the pistons 68B and 69B switch or reverse their directions of movement.

The housing wall 94B also includes the outlet passage 122B that communicates with the pumping chambers 124B and 125B through respective outlet ports 159 which ports are controlled by check valves. The check valves of these outlet ports 159 operate opposite to the above described check valves in that the check valves in ports 159 are normally closed when a vacuum is applied thereto to prevent in-flow, but open in response to pressure within the pumping chambers 124B and 125B to permit out-flow. In this configuration, the reciprocating movement of the piston 68B and 69B effect simultaneous refilling and pumping through the respective inlet passage 121B and outlet passage 122B. This therefore provides a continuous pressure of propane fuel additive being supplied through the supply line 32 to the engine intake 14.

In view of the foregoing, the embodiment of FIGS. 13 and 14 illustrate a mechanically driven pump 19B which still exhibits advantages associated with the barrier fluid configuration.

Although particular preferred embodiments of the invention have been disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention. 

What is claimed:
 1. A multi-piston pump for pumping an engine fluid in a vehicle comprising: a pump housing defining at least first and second piston bores which are separated from each other, each of said piston bores comprising a housing shoulder which faces axially, said piston bores having opposite ends wherein said housing has a drive fluid connector opening into each of said piston bores at said first end, an inlet port opening into each of said piston bores for supplying the engine fluid to said second end, and an outlet port opening into each of said piston bores for discharging said engine fluid from said second end to an engine of the vehicle; at least first and second pistons slidably received within said first and second piston bores respectively so as to each reciprocate axially in opposite axial directions along a pumping stroke and an opposite return stroke, each of said first and second pistons having a piston shoulder facing axially, said piston shoulders and said bore shoulders facing toward each other in opposing relation and being spaced apart to define first and second barrier fluid chambers between said first and second pistons and said first and second piston bores wherein a volume of each of said first and second barrier fluid chambers decreases and increases respectively during movement of said piston through said pumping stroke and said return stroke, said first and second barrier fluid chambers being fluidly connected together wherein said first and second barrier fluid chambers contain a barrier fluid such that decreasing the volume of one said first and second barrier fluid chambers displaces said barrier fluid into and increases the volume of the other of said first and second barrier fluid chambers to fluidly displace the piston within said other of said first and second barrier fluid chambers through the return stroke thereof; a control system for alternatingly pressurizing said first and second piston bores with a drive fluid at said first ends through said drive fluid connectors to alternatingly drive one or the other of said first and second pistons through the respective pumping stroke thereof while the other of said first and second pistons is driven simultaneously through the return stroke thereof by the displacement of said barrier fluid between said first and second barrier fluid chambers, said control system successively pressurizing one of said first and second piston bores and then the other to reciprocate said first and second pistons through their respective pumping and return strokes.
 2. The pump according to claim 1, wherein said outlet port in one said piston bore opens during the pumping stroke of the piston therein for pumping of the engine fluid out of said pump while said inlet port in the other said piston bore opens during the simultaneous return stroke of the piston therein to recharge said other piston bore with said engine fluid.
 3. The pump according to claim 1, wherein each of said piston bores is defined by a stepped interior bore surface which comprises a first bore section having a major bore width, and a second bore section having a minor bore width smaller than said major bore width.
 4. The pump according to claim 3, wherein said bore shoulder is located axially between said first and second bore sections and extends widthwise from said first bore section to said second bore section.
 5. The pump according to claim 3, wherein each of said piston bores is defined by first and second piston sections which have respective major and minor piston widths proximate to said first and second widths of said piston bores.
 6. The pump according to claim 5, wherein said piston shoulder is located axially between said first and second piston sections and extends widthwise from said first piston section to said second piston section.
 7. The pump according to claim 1, wherein said barrier fluid is an incompressible liquid.
 8. The pump according to claim 1, wherein said control system comprises a control valve connected to said drive fluid connectors of said first and second piston bores and being operable between first and second operative conditions, said control valve in said first operative condition pressurizing said first piston bore and depressurizing said second piston bore to respectively move said first and second pistons through their respective pumping and return strokes, and then being switched to said second operative condition and depressurizing said first piston bore and pressurizing said second piston bore to respectively move said first and second pistons through their respective return and pumping strokes.
 9. The pump according to claim 8, wherein said second ends of said piston bores include respective proximity sensors for detecting the approach of each of said pistons during said pumping stroke thereof and switching said control valve between said first and second operative conditions.
 10. The pump according to claim 8, wherein each of said piston bore includes a drive fluid discharge passageway which defines a restricted flow of drive fluid being discharged from said piston bore during said return stroke, said discharge passageway restricting said restricted flow of said drive flow to control a rate of movement of said piston through said return stroke.
 11. The pump according to claim 1, wherein said barrier fluid separates said drive fluid from said engine fluid to define a barrier against leakage of said engine fluid into said drive fluid.
 12. A multi-piston pump for pumping an engine fluid in a vehicle comprising: a pump housing having an outer wall defining at least first and second piston bores which are separated internally from each other by a housing wall, each of said piston bores comprising a stepped interior bore surface defined by a first bore section having a major bore width, a second bore section having a minor bore width smaller than said major bore width, and a housing shoulder which is located axially between said first and second bore sections and extends widthwise from said first bore section to said second bore section so as to face axially, said piston bores having opposite ends wherein said housing has a drive fluid connector opening into each of said piston bores at said first end, an inlet port opening into each of said piston bores at said second end for receiving an engine fluid, and an outlet port opening into each of said piston bores at said second end for discharging said engine fluid to an engine of the vehicle; at least first and second pistons slidably received within said first and second piston bores respectively so as to each reciprocate axially in opposite axial directions along a pumping stroke and an opposite return stroke, each of said first and second pistons having first and second piston sections which have respective major and minor piston widths proximate to said first and second widths of said piston bores and have a piston shoulder, said piston shoulder being located axially between said first and second piston sections and extending widthwise from said first piston section to said second piston section so as to face axially, said piston shoulders and said bore shoulders facing toward each other in opposing relation and being axially spaced apart to define first and second barrier fluid chambers between said first and second pistons and said first and second piston bores, said first and second barrier fluid chambers being fluidly connected together by at least one balancing passage extending through said housing wall wherein said first and second barrier fluid chambers contain a barrier fluid such that decreasing a volume of one said first and second barrier fluid chambers displaces said barrier fluid into and increases a volume of the other of said first and second barrier fluid chambers, a control system for alternatingly pressurizing said first and second piston bores through said drive fluid connectors with a drive fluid, wherein one of said first and second pistons is alternatingly driven through the respective pumping stroke thereof by said control system while the other of said first and second pistons is driven simultaneously through the return stroke thereof by the displacement of said barrier fluid between said first and second barrier fluid chambers, said control system successively pressurizing one of said first and second piston bores and then the other to reciprocate said first and second piston through their pumping and return strokes; said outlet port in one said piston bore opening during the pumping stroke of the piston therein for pumping of the engine fluid out of said pump and said inlet port in the other said piston bore opening during the simultaneous return stroke of the piston therein to recharge said other piston bore with said engine fluid.
 13. The pump according to claim 12, wherein said barrier fluid is an incompressible liquid.
 14. The pump according to claim 13, wherein said barrier fluid effects displacement of each of the first and second pistons through the respective return stroke thereof.
 15. The pump according to claim 12, wherein said control system includes an overpressure detector for detecting excessive pressure of said barrier fluid indicating leakage of said engine fluid or said drive fluid into said barrier fluid chambers.
 16. The pump according to claim 12, wherein said control system comprises a four-way valve connected to said drive fluid connectors of said first and second piston bores for pressurizing said first piston bore and depressurizing said second piston bore in a first operative condition to respectively move said first and second pistons through their respective pumping and return strokes, and then depressurizing said first piston bore and pressurizing said second piston bore in a second operative condition to respectively move said first and second pistons through their respective return and pumping strokes.
 17. The pump according to claim 16, wherein said second ends of said piston bores include respective proximity sensors for detecting the approach of each of said pistons during said pumping stroke thereof and switching said four-way valve between said first and second operative conditions.
 18. The pump according to claim 12, wherein said drive fluid is pressurized air supplied by a vehicle air supply system.
 19. A multi-piston pump for pumping an engine fluid in a vehicle comprising: a pump housing defining at least first and second piston bores which are separated from each other, each of said piston bores comprising a housing shoulder which faces axially, said piston bores having opposite first and second ends wherein said housing has an inlet port opening into each of said piston bores for supplying the engine fluid to said second end, and an outlet port opening into each of said piston bores for discharging said engine fluid from said second end to an engine of the vehicle; at least first and second pistons slidably received within said first and second piston bores respectively so as to each reciprocate axially in opposite axial directions along a pumping stroke and an opposite return stroke, each of said first and second pistons having a inner pumping side and an outer side disposed within said second and first ends of said first and second piston bores, and having a piston shoulder axially between said inner pumping side and said outer side wherein said piston shoulder faces axially, said piston shoulders and said bore shoulders facing toward each other in opposing relation and being spaced apart to define first and second barrier fluid chambers between said first and second pistons and said first and second piston bores wherein a volume of each of said first and second barrier fluid chambers decreases and increases respectively during movement of said piston through said pumping stroke and said return stroke, said barrier fluid chambers axially separating said inner pumping side from said outer side of said first and second pistons, said first and second barrier fluid chambers being fluidly connected together by a balancing passage extending through said housing wherein said first and second barrier fluid chambers contain a barrier fluid such that decreasing a volume of one said first and second barrier fluid chambers displaces said barrier fluid into and increases a volume of the other of said first and second barrier fluid chambers; said first and second pistons including respective axially spaced seals on opposite sides of said barrier fluid chambers which sealingly separate said barrier fluid chambers from said inner pumping side of said pistons and said outer side thereof, said seals sealing against leakage of said engine fluid being pumped into said barrier fluid chambers; and a control system having a drive system to alternatingly drive one or the other of said first and second pistons through the respective pumping stroke thereof while the other of said first and second pistons is driven simultaneously through the return stroke thereof.
 20. The pump according to claim 19, wherein said barrier fluid is an incompressible liquid.
 21. The pump according to claim 20, wherein said barrier fluid lubricates said seals.
 22. The pump according to claim 19, wherein said control system includes an overpressure detector for detecting excessive pressure of said barrier fluid indicating leakage of said engine fluid into said barrier fluid chambers.
 23. The pump according to claim 19, wherein said control system includes a contaminant sensor in communication with said barrier fluid to detect leakage of said engine fluid into said barrier fluid chambers.
 24. The pump according to claim 19, wherein said pump includes a drive fluid connector opening into each of said piston bores at said first end, and said control system pressurizes said first and second piston bores with a drive fluid which drives one of said pistons through said pumping stroke thereof, while said barrier fluid fluidly displaces the piston within said other of said piston bores through said return stroke.
 25. The pump according to claim 24, wherein said drive fluid comprises pressurized air supplied by a vehicle air supply system, and said control system successively pressurizes one of said first and second piston bores and then the other to reciprocate said first and second pistons through their pumping and return strokes, said control system comprising a control valve connected to said first and second piston bores for pressurizing said first piston bore and depressurizing said second piston bore in a first operative condition to respectively move said first and second pistons through their respective pumping and return strokes, and then depressurizing said first piston bore and pressurizing said second piston bore in a second operative condition to respectively move said first and second pistons through their respective return and pumping strokes
 26. The pump according to claim 25, wherein said seals seal against leakage of any leaked engine fluid within said barrier fluid out of said barrier fluid chambers to said outer sides of said pistons.
 27. The pump according to claim 26, wherein said control system includes a contaminant sensor in communication with said drive fluid to detect leakage of said engine fluid into said drive fluid.
 28. A piston pump for pumping an engine fluid in a vehicle comprising: a pump housing defining at least one piston bore comprising a housing shoulder which faces axially, said piston bore having opposite first and second ends wherein said housing has an inlet port opening into each said piston bore for supplying the engine fluid to said second end, and an outlet port opening into each said piston bore for discharging said engine fluid from said second end to an engine of the vehicle; a piston slidably received within each said piston bore so as to reciprocate axially in opposite axial directions along a pumping stroke and an opposite return stroke, said piston having an inner pumping side and an outer side disposed within said second and first ends of said piston bore, and having a piston shoulder axially between said inner pumping side and said outer side wherein said piston shoulder faces axially, said piston shoulder and said bore shoulder of each said piston facing toward each other in opposing relation and being spaced apart to define a respective barrier fluid chamber between each said piston and said respective piston bore wherein a volume of said barrier fluid chamber decreases and increases respectively during movement of said piston through said pumping stroke and said return stroke, said barrier fluid chamber including a barrier fluid disparate from said engine fluid and axially separating said inner pumping side from said outer side of said piston, said pump including a barrier fluid passage for accommodating displacement of said barrier fluid into and out of said barrier fluid chamber; each said piston including respective axially spaced seals on opposite sides of said barrier fluid chamber which sealingly separates said barrier fluid chamber from said inner pumping side of said piston and said outer side thereof, said seals sealing said engine fluid being pumped against leakage into said barrier fluid chamber; and a control system having a drive system to alternatingly drive one or the other of said first and second pistons through the respective pumping stroke thereof while the other of said first and second pistons is driven simultaneously through the return stroke thereof.
 29. The pump according to claim 28, wherein a plurality of said pistons and said piston bores are provided which define respective barrier fluid chambers fluidly connected together by a balancing passage extending through said housing wherein decreasing a volume of one said barrier fluid chambers displaces said barrier fluid into and increases a volume of the other of said barrier fluid chambers
 30. The pump according to claim 29, wherein said barrier fluid lubricates said seals.
 31. The pump according to claim 28, wherein said control system includes an overpressure detector for detecting excessive pressure of said barrier fluid indicating leakage of said engine fluid into said barrier fluid chamber.
 32. The pump according to claim 28, wherein said control system includes a contaminant sensor in communication with said barrier fluid to detect leakage of said engine fluid into said barrier fluid chambers.
 33. The pump according to claim 29, wherein said seals seal against leakage of any leaked engine fluid within said barrier fluid out of said barrier fluid chambers to said outer sides of said pistons. 